A successful coherent light-emitting device should be designed to efficiently convert energy from an electric source by means of an active medium to the desired frequency of coherent light.
In order to meet the design criteria of a successful coherent light-emitting device various lasers have been developed. For example, The Ruby Laser, developed by Maiman, U.S. Pat. No. 3,353,115. Is a device, which incorporates a flash lamp, wrapped around a synthetic ruby with a mirror on each end. The ruby laser emitted light in short, intense pulses of a single wavelength.
U.S. Pat. No. 2,929,922 issued to Townes and Schawlow describes a gas laser, which employs a glass tube, filled with a gas, carbon dioxide, neon, helium or both. An electrical power supply charges electrodes, which electrifies the gas, causing spontaneous emissions throughout the medium. A population inversion occurs when spontaneous emissions are trapped between a rear mirror and an output mirror. The population inversion is a coherent beam of light, which immerges at the output mirror. The sealed gas tube requires periodic replacement of the laser gas because contaminants accumulate and gradually degrade laser action.
A Symmetrically Conductive Device and Method of making the same is U.S. Pat. No. 2,994,018 issued to Hall for a semiconductor laser device and a manufacturing process for the same. The semiconductor laser creates light when electrons from an electrical source travel through the N-type layer, across the junction layer to the P-type layer, making a circuit. Light is generated from the re-combination of electron-hole pairs at the forward-biased junction layer. Cleaving a wafer into chips exposing the junction layer makes the laser. The cleaving process forms facets. The facets reflect only about 30% of the light back into the junction layer. However, enough light is reflected back into the junction layer to allow stimulated emissions for a population inversion. The laser is packaged in a way, which allows the beam to emerge from only one end of the laser.
The output of coherent light is very inefficient in a semiconductor laser and much energy in the drive current is lost as heat.
Stimulated Emission of Radiation in Periodically Deflected Electron Beam is U.S. Pat. No. 3,822,410 issued to Madey. The device is a tunable generator or amplifier of coherent radiation in the infrared, optical, ultra-violet and x-ray regions. A relativistic electron beam is periodically deflected by a transverse magnetic field defined by a linear array of adjacent magnets having opposing polarities. Each time the electron beam is deflected by a change in polarity, it emits a burst of radiation. A mirror at one end of the linear cavity and a partially reflective mirror at the other end of the cavity reflect the burst of radiation to create a coherent beam of radiation.
The electron accelerator used to generate the electron beam can be rather bulky as respects to the output in wattage of coherent radiation. The linear array of magnets is also quite large and heavy. The efficiency of the tunable generator of coherent radiation is roughly from 20 to 50 percent.
The Free-Electron Amplifier device with Electro-magnetic radiation Delay Element is U.S. Pat. No. 4,529,942 issued to Patel and Shaw is a free-electron laser consisting of a rather large external accelerator, which injects an electron beam a distance to an injection magnet, which aligns the beam to the optical axis of the laser cavity. An extraction magnet guides the electron beam away from the laser cavity. The laser cavity is the source of a helical magnetic field comprising of several relatively large electrical conductors fastened to a support cylinder, which serves to impart transversal acceleration to the electrons of the beam. Wire meshes insides the support cylinder form a resonant filter, which serves as a delay element. A semi-transparent mirror is at one end of the laser cavity and a mirror is at the other end. The device operation results in a modicum of coherent radiation being emitted through the semi-transparent mirror relative to the device size.